Solution
Initialization VIIt runs in the background when the custom device is first added to the system definition. The initialization page does not run again unless the operator removes and re-adds the custom device.
Main Page VIIt runs whenever the operator clicks on the on the custom device’s top-level item in System Explorer’s configuration tree.
RT Driver VIIt defines the behavior of the custom device on the
execution host. The RT Driver VI runs on the execution host regardless of the target’s operating system.
Constants VIIt is basically a global variable that is used to share data across the custom device.